Slip-ring sealing structure in a centrifugal pump



Jan. 6, 1970 E. EGGE 3,487,775

SLIP-RING SEALING STRUCTURE IN A CENTRIFUGAL PUMP Filed Sept. 5, 1968 United States Patent 3,487,755 SLIP-RING SEALING STRUCTURE IN A CENTRIFUGAL PUMP Emile Egger, Cressier, Switzerland, assignor to Emile Egger dz C0. AG, Cressier, Neuchatel, Switzerland Filed Sept. 5, 1968, Ser. No. 757,557

Claims priority, application Switzerland, Sept. 23, 1967,

13,301/ 67 Int. Ql. Ftidd 29/12; F16 /40, 15/16 US. Cl. 103-4111 8 Claims ABSTRACT OF THE DISCLGSURE This invention relates to slip-ring sealing structure in a centrifugal pump, having a first slip-ring fixed on the pump shaft and a second slip ring suspended at the pump casing by means of an annular membrane allowing axial displacement of the second slip ring. A number of slip-ring sealing assemblies of this type are known, whereby it has also been suggested to insert annular spring elements into such membranes for elastically urging the axially movable slip ring against the slip ring fixed on the pump shaft. In these prior systems the pressure at the rear side of the pump impeller directly acts onto the one side of the annular membrane, whereby the force by which the slip rings are urged against each other is subject to variations according to the value and direction of the fluid pressure at the rear side of the impeller.

Experience has shown that these and all other prior sealing structures are only suitable for use with clean fluids. With these structures it is impossible to avoid small relative axial displacement and spacing of the slip rings from each other and entering of small particles of charged or contaminated mediums such as sandy suspensions, koalin suspensions, pulp or the like between the slip rings. Another drawback of the prior systems resides in the impossibility to properly cooling the slip rings in view of the variations of the force with which the slip rings are urged against each other due to the pressure variations at the rear side of the impeller acting on the annular membrane mentioned above.

This invention aims in providing a reliable and cheap slip-ring sealing structure wherein the slip rings are urged against each other with substantially constant pressure such that the slip rings cannot be spaced from each other and entrance of small particles suspended in the medium to be pumped between the slip rings is prevented. The slip-ring sealing structur according to this invention boardly comprises a slip ring fixed on the pump shaft and a slip ring suspended at the pump casing by means of an annular membrane, this membrane and second membrane means being each disposed between the space at the rear side of the pump impeller and a pressure space filled with pressure fluid, whereby the pressure at the rear side of the impeller simultaneously acts at one side of said annular membrane directly and at the other side through said second membrane means and pressure space respectively. Through said second membrane means and the pressure chamber filled with fluid the pressure existing at the rear side of the impeller is also transmitted to and acts on the rear side of the annular membrane carrying the one slip ring. In this way the influence of the pressure existing at the rear side of the impeller onto the annular membrane carrying the one slip ring may practically be compensated so that the slip rings may be urged against each other with a constant pressure produced by spring action or any other means. Preferably means may be provided for particularly etficient cooling of the slip rings. It is a particular object of this invention to build up a counter-pressure at the side of the slip rings opposite to the medium to be pumped, this counter-pressure being preferably maintained at a value somewhat higher than the highest value of pressure to be expected in the space at the rear side of the impeller. In this way lubrification of the slip rings will always be eflected by the clean medium admitted to the rear side of the slip rings and not by the contaminated medium to be pumped.

This invention will now be explained in detail with reference to an embodiment illustrated by way of example in the accompanying drawing.

The drawing shows an axial section of the important parts of the pump. An impeller 2 is fixed on the pump shaft 1. This impeller has release apertures 3 opening radially into the canals 4 of the impeller 1, wherein the medium to be pumped flows in substantially radial direction. An annular carrier 5 is clamped. between the hub of the impeller and a shoulder of shaft. 1, a first slip ring- 6 with a slip pad 7 being fixed on carrier 5. Slip pad 7 contacts the slip pad 9 of another slip ring 8 fixed in a flange portion 10 at the one end of a sleeve 11. The other end of sleeve 11 is axially displaceably guided in a bore of the pump casing and is sealed in this bore by means of a sealing ring 12. A ring 11a is inserted into the same bore and sealed therein by means of a sealing ring, this ring 11a carrying a separating tube 13 maintained in coaxial position within the sleeve 11 by means of bosses 13a engaging the inner surface of sleeve 11. The separating tube 13 extends from the ring 11a into the space inside slip ring 6 and thus subdivides the annular space between sleeve 11 and shaft 1 into two coaxial annular spaces 14 and 15 communicating with each other inside the slip ring 6. The outer space 15 communicates through a bore 16 of sleeve 11 with a duct 17 having a threaded portion 18 at its outer end for connection of a fluid conduit. The inner annular space 14 communicates with a duct 19 outside ring 13, duct 19 having also a threaded portion 20 for connection of a fluid conduit. The annular space 14 and the duct communicating therewith are sealed by means of a sealing ring 22 inserted in a flang portion 21 of the casing.

The sleeve 11 and flange portion 10 are connected in sealing condition to a flexible membrane 23 of rubber, plastics material or the like, of which the outer rim is clamped between rings 24 and 25 of the pump casing. Due to its flexibility the membrane 23 allows limited axial displacement of the flange 10, of sleeve 11 and of the slip ring 8 supported thereon. An annular pressure chamber portion 26 is formed outside the annular membrane 23, this pressure chamber portion communicating through bores 27 of the casing and of ring with another annular chamber portion 28 which communicates through bores 29 of the pump casing with a third annular chamber portion 30. Annular chamber portion 30 is separated from the space at the rear side of the impeller by means of a flexible membrane 31 similar to membrane 23. The annular chamber portions 26, 28 and 30 and the bores interconnecting them are completely filled with a practically incompressible fluid, preferably oil. The filling opening 32 of these communicating chambers, which is shown in open condition in the drawing, is usually closed by means of a sealing screw. By inserting this screw more or less into the bore 32, a certain overpressure may be produced in the pressure chamber 263t).

A tube 33 is fixed on a shoulder at the rear side of the impeller, this tube 33 extending rearwardly over the slip rings and thus forces fluid flowing from the rear side of the impeller through the release apertures 3 to circulate over the slip rings thereby providing for eflicient cooling of the same.

A pressure spring 34 acts between the casing and the inner rim of the membrane 23 for urging the slip ring 8 against slip ring 6.

Operation of the illustrated pump is as follows:

During normal operation of the pump overpressure is produced at the rear side of the impeller, this overpressure being built up by fluid leaking from the outer ends of the impeller canals through the gap between the impeller wall and the pump casing. This overpressure at the rear side of the impeller sets up a fluid circulation rearwardly along the tube 33, and through the tube 33 towards the impeller, through the release aperture 3 back into the impeller canals. This circulation provides for eflicient cooling of the slip rings and of the parts supporting them. It was found that due to the exit direction of the release bores 3 substantially in the direction of the impeller flow, that is radially outwards in the radial impeller illustrated in the drawing, the above cooling circulation is intensified and additionally a substantial increase of the pump pressure is obtained compared with the pressure of similar pumps having release bores ending in substantially axial direction at the front side of the impeller.

The pressure built up at the rear side of the impeller is transmitted through the flexible membrane 31 to the fluid contained in the pressure chamber 26-30, and consequently this pressure is transmitted tothe rear side (right side in the drawing) of the membrane 23. The surfaces at the front and rear side of the membrane 23 whereon the pressure at the rear side of the impeller acts directly and indirectly through membrane 31 and pressure chamber 26-30 respectively, are so dimensioned that the forces acting on the membrane 23 practically compensate each other and that under all circumstances the pressure acting directly from the rear side of the impeller onto the left side of membrane 23 will never exceed the pressure acting in opposite direction from the pressure chamber 2630 so that there is no danger for slip ring 8 being lifted off slip ring 6. Therefore, the pressure, by which the slip rings are urged against each other is practically constant and determined by the pressure of spring 34. Pressure variations in the space at the rear side of the impeller are immediately transmitted through membrane 31 and pressure chamber 2630 to the rear side of membrane 23 so that no appreciable changes of the pressure acting between the slip rings will occur. As mentioned above, the fluid in the pressure chamber 2630 may have a certain overpressure or bias pressure, in which case fluid pressure acting on membrane 23 is added to the pressure of spring 34 for urging the slip rings against each other. Nevertheless pressure variations at the rear side of the impeller are transmitted through membrane 31. and

pressure chamber 26-30 to the membrane 23 so that pressure fluctuations at the rear side of the impeller are without eifect on the contact pressure of the slip rings.

When particularly eflicient cooling of the slip rings and especially of their pads 7 and 9 is wanted, circulation of a cooling medium through ducts 17 and 19 may be set up. In this case, cooling water may be admitted through duct 19 through the inner annular space 14 forewardly, round the fore edge of tube 13 and returns along the inner side of the slip rings back through the outer annular space 15 and duct 17. Water from the town water supply may be used. However, a closed circulation of cooling fluid may also be set up by means of a circulating pump, and in this case oil may also be used as a cooling medium. In any case it is possible to admit the cooling medium at a certain overpressure, this overpressure preferably exceeding the maximum overpressure to be expected at the rear side of the impeller so that there will always exist a pressure difference at the sealing gap of the slip rings in a direction from the cooling medium inside the slip rings towards the medium at the rear side of the impeller. Therefore, the cooling medium tends to leak between the pads 7 and 9 of the slip rings outwardly into the pump space, but the medium contained in the pump space will not leak in opposite direction into the cooling circuit. It is thus possible to so control the pressure in the cooling circuit that the slip rings are lubricated by clean cooling medium and not so by contaminated medium from the pump space. Obviously, care must be taken that a cooling medium is used which is compatible with the medium to be pumped. If efl-icient cooling is not required, the cooling medium must not be circulated, in which case the one duct 18 or 20 may be shut off and the other may be connected to a suitable pressure source adapted to maintain the static pressure in the annular spaces 14 and 15 but does not circulate the cooling medium.

What I claim is:

1. A slip-ring sealing structure in a centrifugal pump, comprising a pump shaft, a first slip ring fixed on the pump shaft, a pump casing, a second slip ring axially displaceably suspended on the pump casing by means of a first annular membrane, an impeller and a space formed between the rear side of the impeller and the pump casing, second membrane means having one side thereof facing said space of the rear side of the impeller, and a pressure chamber formed in said casing, the other side of said second membrane and one side of said annular membrane facing said pressure chamber; and means for biasing said second slip ring into engagement with the first slip ring.

2. A sealing structure according to claim 1, comprising spring means urging said second slip ring against said first slip ring fixed on the pump shaft.

3. A sealing structure according to claim 1, comprising fluid under pressure in said pressure chamber.

4. A sealing structure according to claim 1, comprising release apertures and flow canals in said impeller, said release apertures opening into said flow canals substantially in the direction of fluid flow in said canals.

5. A sealing structure according to claim 4, comprising a tube fixed at the rear side of the impeller outside said release apertures and extending rearwards from the impeller coaxially to the impeller shaft, said slip rings being located inside said tube.

6. A sealing structure according to claim 1, comprising an annular space formed between the slip rings and the pump shaft, this annular space communicating with at least one fluid connection at the pump casing.

7. A sealing structure according to claim 6, com-prising a tubular separating wall axially extending through said annular space, said annular space being thereby subdivided into an inner and an outer portion communicating each with a separate fluid connection at the pump casing.

8. A sealing structure according to claim 7, comprising a sleeve carrying said. se ond slip ring at one end and said tubular separating Wall at its other end, said other end of the sleeve being displaeeably guided in sealing condition in the pump casing.

References Cited UNITED STATES PATENTS E FOREIGN PATENTS 228,945 5/ 1924 Great Britain. 625,898 7/1949 Great Britain. 729,327 5/ 1955 Great Britain.

HENRY F. RADUAZO, Primary Examiner U.S. Cl. X.R. 277-3, 27 

